Disjoint and coextensive amminium radical cations: a general problem in making amminium radical cation based high-spin polymers

Article abstract of DOI:10.1016/j.tet.2007.08.038

A two-electron oxidation of N,N,N′,N′-tetrakis(2-methoxyphenyl)-1,3-diaminobenzene 12 gives the diradical dication 12^{2{radical dot}+}, which is an aza analogue of the Schlenk hydrocarbon and, like the Schlenk hydrocarbon, has a triplet ground st

Full text of DOI:10.1016/j.tet.2007.08.038

Tetrahedron 63 (2007) 11458–11466
Disjoint and coextensive amminium radical cations: a general
problem in making amminium radical cation based
high-spin polymers
*
Richard J. Bushby, Colin A. Kilner, Norman Taylor and Matthew E. Vale
Self-Organising Molecular Systems (SOMS) Centre, University of Leeds, Leeds LS2 9JT, UK
Received 15 May 2007; revised 23 July 2007; accepted 10 August 2007
Available online 15 August 2007
ꢀ
Abstract—A two-electron oxidation of N,N,N0,N0-tetrakis(2-methoxyphenyl)-1,3-diaminobenzene 12 gives the diradical dication 122 +
,
which is an aza analogue of the Schlenk hydrocarbon and, like the Schlenk hydrocarbon, has a triplet ground state. However, an attempt
to produce pentuplet tetraradical tetracations by extending the same ferromagnetic spin-coupling motif in a linear or a cyclic fashion was
unsuccessful. Two-electron oxidations to give disjoint diradical dications (in which the charges and spins are spatially separated) are relatively
easy but it proved impossible to remove the third and fourth electrons. This would require generation of coextensive radical ions in which the
charges and spin distributions overlap. The results obtained with these model oligomers illustrate what is a general problem in the creation of
high-spin polymers in which the spin-bearing centres are amminium radical cations. Strong ferromagnetic spin-coupling depends on the for-
mation of coextensive rather than disjoint radical cations but the formation of coextensive radical cations with strong ferromagnetic coupling
involves a large additional coulombic penalty.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
roughly parallel each other. As a result hole/hole repulsion in
1b is also much larger than hole/hole repulsion in 3b and it
is much harder to form 1b by a two-electron oxidation of 1d
than to form 3b by a two-electron oxidation of 3d.17 Hence it
is fundamentally difficult to get both strong exchange
interaction and easy formation of the amminium radical cat-
ion. Another problem which is similar in nature, and which
is the main theme of this paper, is illustrated in Figure 2.
Taking the example of the amminium radical cation based
Most attempts to make high-spin polymers1–5 have used the
trityl radical1,2,6 or the isoelectronic triphenylamminium
radical cation4,5,7–13 as the spin-carrier and ferromagnetic
coupling, which is 1,3-through benzene (1a, 1b), 3,40-
through biphenyl (2a, 2b) or 4,400-through metaterphenyl
(3a, 3b) (Fig. 1). Each of these three ferromagnetic spin-
coupling motifs14 is based on that of a triplet ground state
quinodimethane (1c–3c).15 p-Biradicals can be classified
as either disjoint (having spin distributions that are spatially
separated) or coextensive (having spin distributions that
overlap in space). Hund’s rule only applies to coextensive
systems1,4 and all of the biradicals 1–3 are of the coextensive
type. In such systems it is the extent to which the spin distri-
butions overlap in space that determines the strength of the
exchange interaction.1,13,16 Hence, in passing along the
series 1/2/3 this overlap falls off quite sharply and so
does the strength of the exchange interaction. As a result
the singlet/triplet splitting in 115 is much larger than that
in 3.13 This creates a problem when exploiting amminium
ion based species. In these, the charge and spin distributions
ꢀ
polymer 5x +, which would be formed by (oxidative) p-dop-
ing of the corresponding arylamine 4, the sequence of oxida-
tion steps is determined by electrostatics. Removal of
electrons from alternate sites, to give a polymer such as
ꢀ
5
n +, should be relatively easy. In this there is no overlap
ꢀ
of the spin (and hole) distributions and 5n + would be of
low spin. Such systems where there is no overlap (or essen-
tially no overlap) in the spin distributions are said to be dis-
joint. To create a coextensive high-spin polymer such as
ꢀ
52n + there is clearly an additional coulombic ‘penalty’.
Not only are the charged centres close together but the
charge distributions actually overlap. In this paper the extent
of this problem is explored using a series of model ‘1,3-
through benzene’ oligomers 12–14. We show that this
coulombic ‘penalty’ is quite severe and, that although
it is easy enough to get the low spin disjoint systems, oxida-
tion to the coextensive high-spin systems is very difficult
indeed.
Keywords: High-spin polymer; Polyarylamine; Triplet; Quinodimethane;
Radical cation; Cyclic voltammetry; Magnetometry.
* Corresponding author. Tel.: +44 (0)113 3436509; fax: +44 (0)113
3436452; e-mail: r.j.bushby@leeds.ac.uk
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.038

R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
11459
S
S
n/2
n/2
S
S
1
2
N
Ph
N
Ph
N
Ph
N
Ph
a, S = CPh2
b, S = N+Ph2
4
-
-ne : relatively 'easy'
c, S = CH2
S
a
S
+
disjoint
d, S = NPh2
3
or
or
-a -a
a
2a
a
-a -a
2a
a
n/2
-a
-a
-a
-a
-a
-a
-a
-a
N
N
N
N
Ph
Ph
Ph
Ph n/2
n.+
a
5
a
χB , a = 1/√13
χA , a = 1/√13
-
-ne : relatively 'difficult'
coextensive
2c
-2c
-2c
c
-c
2c
b c
-b
2b -2b 2b
-c
-b
b
-b
-c
-b
c
-b
-c c
c
-b
-b
-c
n/2
-b
-c
χ17 = x.(χA - χB ), c = 1/√28
c
b
b
N
Ph
N
Ph
N
Ph
N
Ph
χ16 = x.(χA + χB ), b = 1/√24
n/2
2n.+
Figure 1. Top: the simplest ‘building blocks’ 1–3 that are used for the con-
struction of high-spin polymers. In formulae 1–3 the ring in which the spin
distributions overlap (are coextensive) is shown in bold. Bottom: formal deri-
vation of the degenerate Huckel NBMOs of the Schlenk hydrocarbon 1a
from the NBMOs of two trityl radicals. The application of Hund’s rule
requires that the singly occupied orbitals are degenerate, orthogonal and
coextensive. In high-spin atom-based centres (carbenes, transition metal
centres, etc.) all three of these requirements are always met. In molecular
systems even when the orbitals are degenerate and orthogonal they are
not always coextensive. In non-coextensive (disjoint) molecular systems
‘Hund’s’ rule no longer applies.
5
ꢀ
Figure 2. A hypothetical linear high-spin polymer 52n + based on the repeat
unit 1b illustrating the problem associated with the formation of coextensive
spins. As in all such polymers and oligomers, the amminium ion centres are
generated by p-doping (oxidative doping) of the corresponding polyaryl-
amine. Note that each spin is only coextensive with its nearest neighbour,
otherwise they are disjoint. Only the coextensive spin distributions give fer-
romagnetic coupling but formation of coextensive spin distributions incurs
an additional coulombic penalty.
reversible one-electron transfer. Similarly, UV/visible/near
IR spectroscopic studies of the oxidation in dichloromethane
using thianthrenium tetrafluoroborate (THBF4)27 as the oxi-
dant showed that there is a clean one-electron oxidation and
clear isosbestic points (Fig. 4). The 4.07 eV band of the
amine decreases reaching a limit exactly upon addition of
1 equiv of the oxidant. Addition of more than 1 mol of oxi-
dant produces no change in the spectrum other than a buildup
of bands due to the oxidant itself. The spectrum obtained for
the radical cation 11ꢀ+ is very similar to that of the radical
cation of tris(4-methoxyphenyl)amine and the D0–D1 transi-
tion is split (1.35 and 1.50 eV).28 The oxidised solution is
blue-green. EPR spectroscopic studies also confirmed that
there is clean formation of the radical cation and that this
is stable in solution for many hours. The spectrum of the radi-
cal cation 11ꢀ+ in dichloromethane at room temperature
shows a 1:1:1 triplet centred at 3351G (a (14N) 8.1G).29
2. Results
2.1. Synthesis
The synthesis of the oligomers is shown in Scheme 1. As well
as the diamine 12, which is the precursor to the triplet dirad-
ꢀ
ical dication 122 +, we have made both linear 137,8 and cyclic
142,18 tetraamines, which should act as precursors to pentu-
plet tetraradical tetracations. Other than for the synthesis
of the monoamine 11,19 palladium catalysed reactions were
used for the key aryl ring–nitrogen bond forming steps.20
2.2. One-electron oxidation of the monoamine 11
The rate of dimerisation of the radical cation 11ꢀ+ is known21
and it is known to give hexamethoxybenzidine.21–25 Hence
we were able to chose conditions for the conversion of 11
to its radical cation 11ꢀ+ in solutions that were sufficiently di-
lute for dimerisation to be very slow. The deconvoluted cy-
clic voltammogram of the amine 11 (Fig. 3a)26 shows one-
electron oxidation and reduction steps, which are well
matched in amplitude confirming that there is a chemically
2.3. One-electron and two-electron oxidation of the
diamine 12
The geometry of the diamine 12 shown in Figure 5 was de-
rived from a single crystal X-ray diffraction study. As

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R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
OMe
MeO
OMe
NH2
N
(i)
OMe
11
6
(ii)
MeO
H
N
OMe
(iii)
N
N
OMe
OMe
OMe
OMe
7
12
(iv) or (v)
MeO
MeO
N
H
N
H
OMe
8
N
N
N
N
OMe
OMe
OMe
OMe
OMe
(vi)
13
MeO
N
N
(vii)
OMe
Br
Br
9
OMe
N
MeO
N
(viii) or (ix)
MeO
(x)
N
N
N
N
OMe
N
H
N
H
MeO
14
OMe
OMe
OMe
10
Scheme 1. Synthesis of the amines 11–14. Reagents and conditions: (i) 2-iodomethoxybenzene/Cu/Na2CO3/ortho-dichlorobenzene/48 h/180 ꢂC/40%; (ii) 2-
iodomethoxybenzene/Pd(OAc)2/PtBu3/tBuONa/toluene/12 h/100 ꢂC/85%; (iii) 1,3-dibromobenzene/Pd(OAc)2/DPPF/tBuONa/toluene/36 h/100 ꢂC/78%; (iv)
3 equiv 1,3-dibromobenzene/Pd(OAc)2/PtBu3/tBuONa/toluene/12 h/100 ꢂC/52%; (v) 3 equiv 1,3-dibromobenzene/Pd(OAc)2/DPPF/tBuONa/toluene/24 h/
100 ꢂC/80%; (vi) large excess of 1,3-dibromobenzene/Pd(OAc)2/DPPF/tBuONa/toluene/24 h/100 ꢂC/70%; (vii) compound 8/Pd(OAc)2/PtBu3/tBuONa/tolu-
ene/18 h/100 ꢂC/83%; (viii) 3 equiv 2-aminomethoxybenzene/Pd(OAc)2/PtBu3/tBuONa/toluene/24 h/100 ꢂC/90%; (ix) 3 equiv 2-aminomethoxybenzene/
Pd(OAc)2/DPPF/tBuONa/toluene/24 h/100 ꢂC; (x) 1 equiv 1,3-dibromobenzene/Pd(OAc)2/PtBu3/tBuONa/dilute solution in toluene/10 days/25 ꢂC/55%.
expected, the nitrogens are almost planar and there is a pro-
peller-like arrangement of the surrounding phenyl rings.9,30
Whereas a one-electron oxidation of 11 gives a trimethoxy-
lated triphenylamine radical cation, the electrophore of 12 is
effectively a dimethoxylated triphenylene. As a result, the
oxidation potential of 12 is higher than that of 11 (Table 1),
the radical cation 12ꢀ+ is less stable and it dimerises more
rapidly.23 We found that, using concentrations similar to
those for the monoamine 11, dimerisation was a significant
factor, particularly for the CV studies since these required
the most concentrated solutions. As shown by the unmatched
areas for the CV peaks in the forward and reverse sweeps
(Fig. 3b), oxidation is not chemically reversible. Further-
more, after the first anodic sweep, subsequent sweeps reveal
new peaks at 0.48 Vand 1.03 V, which can be assigned to the
first and second oxidations of the dimer (benzidine), respec-
tively.21–25 These grow in size with repeated sweeps. The
first oxidation step leading from the monoradical monoca-
tion 12ꢀ+ is at 0.73 V (vs silver/silver chloride) but the sec-
ꢀ
ond leading to the diradical dication 122 + is >1.3 V. This
is unexpectedly high since for N,N,N0,N0,N00,N00-hexakis(4-
methoxyphenyl)-1,3,5-triaminobenzene the first oxidation
potential is at 0.67 V and the second at 0.87 V (ꢁ78 ꢂC,
CH2Cl2, tetrabutylammonium tetrafluoroborate, vs SCE).31
For N,N0-bis[4-(diphenylaminophenyl)]-N,N0-diphenyl-1,3-
diaminobenzene the first oxidation potential is at 0.54 V
and the second at 0.68 V (CH2Cl2, tetrabutylammonium
tetrafluorophosphate, vs SCE).29 For N,N0,N00-tris[4-(diphe-
nylaminophenyl)]-N,N0,N00-triphenyl-1,3,5-triaminobenzene
the first oxidation potential is at 0.59 V and the second at

R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
11461
Figure 5. Geometry of N,N,N0,N0-tetrakis(2-methoxyphenyl)benzene-1,3-
diamine 12 obtained from the single crystal X-ray structure determination.
Ellipsoid probability is 50%.
vs SCE).32 That is in 12 the separation between first and sec-
ond oxidation potentials is >0.57 V whereas in closely re-
lated compounds it is <0.2 V. Tentatively, we ascribe the
exceptional difficulty of removing a second electron from
ꢀ
122 + to a steric effect specific to the ortho methoxy substit-
uents. In dichloromethane these amminium ions are contact
ion paired rather than being present as free ions or solvent
separated ion pairs17 and, as in other trityl systems,33 the
counterion in the contact ion pair would most stably bridge
the central nitrogen and one of the ortho carbons. This may
not be possible in the ortho-methoxylated systems. As can
be seen from Figure 5, the methoxy groups partly ‘cover’
the nitrogen. They will inhibit the approach of the counterion
and this steric hindrance to ion pairing would significantly
reduce the ability of the anion to shield out cation–cation re-
pulsion. The EPR studies of the monocation 12ꢀ+ show that,
at the lower concentration used, dimerisation is slower but
still significant. The initial spectrum shows a 1:1:1 triplet
centred at 3352G (a (14N) 8.1G).29 However, after 30 min
at room temperature a 1:2:3:2:1 quintet centred at 3352G,
(a2ꢃ (14N) 5.9G) develops, which is assigned to the mono-
radical of the benzidine.34 The dimerisation is associated
with a characteristic colour change from blue-green to
deep green. The concentration used for the UV/visible/
near IR spectroscopic studies was <10ꢁ2 times than that
used in the CV studies (<10ꢁ1 times than that used in the
Figure 3. Cyclic voltammograms in dichloromethane with 0.1 M TBAHFP
as supporting electrolyte relative to Ag/AgCl. Sweep rate of 500 mV sꢁ1. (a)
Deconvoluted dI1/dE voltammogram for 1 mM solution of monoamine 11.
(b) Deconvoluted cyclic voltammogram for 1 mM solution of diamine 12
after several cycles. The peaks at ꢁ0.42 V, 0.48 V and 1.03 V associated
with benzidine formation are initially very weak but build up over time.
0.72 V (CH2Cl2, tetrabutylammonium tetrafluorophosphate,
vs SCE)32 and for N,N0,N00-tris[4-(di-para-anisylamino-
phenyl)]-N,N0,N00-tri-para-anisyl-1,3,5-triaminobenzene the
first oxidation potential is at 0.41 V and the second at
0.54 V (CH2Cl2, tetrabutylammonium tetrafluorophosphate,
NAr3
Table 1. Summary of CV data for the model compounds 11–14 in dichloro-
methane with 0.1 M tetrabutylammonium hexafluorophosphate as the sup-
porting electrolyte
+
NAr3
Amine
Potential (V)
E30
E10
E20
E40
11
12
13
14
0.69a
0.73b
0.73c
0.79a
—
—
1.12
>1.3
>1.3
0.87
>1.3
>1.3
0.97d
Half-wave potentials E0 are corrected to the ferrocene/ferrocenium couple,
which is assumed to be +0.50 V under these conditions.
a
Width at half height 70 mV.
Width at half height 45 mV.
Width at half height 50 mV.
b
c
Figure 4. UV/visible/near IR spectra for the oxidation of the monoamine 11
to the radical cation 11ꢀ+ using THBF4 in dichloromethane as the oxidant at
room temperature.
Width at half height 110 mV. Only the E01 peak for the monoamine 11
shows full chemical reversibility.
d

11462
R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
EPR studies) and so dimerisation should be 104–105 times
(102–103 times) slower. Essentially dimerisation is not
a problem. As shown in Figure 6, when the diamine 12 is
reacted with 1 equiv THBF4 in dichloromethane the absorp-
tion band at 4.16 eV decreases by about half of the expected
maximum amount (compare Figs. 6 and 4) when 1 mol of
oxidant is added. The clear isosbestic points indicate a clean
oxidation to the monoradical monocation 12ꢀ+. Since the
thianthrene/thianthrenium couple has a redox potential of
1.1–1.3 V35 it is only useful for electron removal up to this
limit. As a result, on adding a second molar equivalent of ox-
ꢀ
idant, 122 + is not formed and the only change observed is
due to the buildup of THBF4. To make the dication diradical
of 12, a stronger oxidant than THBF4, NOBF4 had to be used
and, to minimise dimerisation, very dilute solutions and low
temperatures. Hence, when a 10ꢁ3 M solution of 12 is
treated with an excess of NOBF4 at 0 ꢂC, followed by rapid
removal of the solvent (also at low temperatures) the solu-
tion retains the characteristic blue-green colouration of the
simple amminium ion chromophore and the diradical dica-
ꢀ
tion 122 + is obtained. This is stable in the solid state. Mag-
netometry shows that cT is temperature independent in the
range 5–250 K although, below 5 K, cT increases and there
is a slight upturn in the 1/c versus temperature plot, this is
(a)
ꢀ
Figure 7. (a) Details of the ‘Curie’ plot (1/c vs T) of solid 122 + 2BF4ꢁ be-
tween 2 and 15 K. (b) Normalized magnetisation against field over temper-
ature (M/Msat vs H/T) at 2 K compared to Brillouin function for S¼1 (upper,
solid line) and S¼1/2.
probably due to weak intermolecular antiferromagnetic in-
teractions (the relevant detail of the plot is shown in
Fig. 7a). The plot of M/Msat versus H/T fits a Brillouin func-
tion for a triplet, S¼1 as shown in Figure 7b. As with other
aza analogues of the Schlenk hydrocarbon,36 the ground
(b)
ꢀ
state 122 + is a triplet.
2.4. Attempted four-electron oxidation of the
tetraamines 13 and 14
The CVs of the tetraamines 13 and 14 are similar to those ob-
tained for the diamine 12 in that the intermediate radical cat-
ions rapidly dimerise and that it is very difficult to remove all
four electrons. As shown in Table 1, the first oxidation poten-
tial for compound 13 is similar to that of the diamine 12 but
that of 14 is a little higher since the electrophore has one less
stabilising methoxy substituent.23 Small new peaks build up
during repeated cycles corresponding to benzidines.21–25
Parallels to the diamine 12 also emerge in the UV/visible/
near IR spectroscopic studies. When a solution of the tetra-
amine 13 is treated with 1 equiv of THBF4, the absorption
band at 4.13 eV decreases by about a quarter of the maxi-
mum expected and further upon addition of the second
equivalent of oxidant. Upon addition of the third and fourth
Figure 6. UV/visible/near IR spectra for the oxidation of the diamine 12
using (a) one molar equivalent and (b) a second molar equivalent of THBF4
in dichloromethane at room temperature. In (b) the dotted line shows the
spectrum of the unoxidised diamine.

R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
11463
equivalents of oxidant there is almost no change. The mono-
through benzene system 12 the charge distributions are cen-
tred closer together and they overlap much more leading to
a difference between the first and second oxidation poten-
tials, which is >0.47 V. Since the tetraamines 13 and 14
are structurally very similar to 12, and since for these the dif-
ferences between first and second oxidation potentials are
only 0.14 Vand 0.18 V, we can safely argue that the dication
ꢀ
radical cation 13ꢀ+ and diradical dication 132 + are formed
but THBF4 is not a sufficiently strong oxidant to remove
the third and fourth electrons. The tetraamine 14 behaves
very similarly. Attempts to establish that high-spin species
were formed by the oxidation of 13 or 14 with excess
NOBF4 followed by rapid solvent removal (using the same
procedure as for the magnetometry studies of 12) all failed.
Only S¼1/2 species can be detected. It seems either that the
requisite polycations cannot be formed using NOBF4 or that
they dimerise much more rapidly.
ꢀ
ꢀ
diradicals 132 + and 142 + have the disjoint structures shown
in Figure 8. In these the charges are far apart from each other
as possible and there is no overlap in the hole distributions.
ꢀ
(In the case of 132 + this would also be the favoured structure
since the electrophore with two methoxy substituents is
slightly easier to oxidise than that with just one.) They would
all be low spin species. The formation of high-spin coexten-
3. Discussion
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
sive species such as 122 +, 133 +, 134 + or 143 +, 144 + involves
ꢀ
ꢀ
As shown in Figure 8, amminium ion analogues of non-
ꢀ
oxidation potentials >1.3 V. The oligomers 13n + and 14n +
are good models for the equivalent polymers and the prob-
lems that are likely to be encountered. When a neutral poly-
arylamine is doped, the sites of doping are principally
determined by electrostatics. Hence in the initial stages
4,14,15
Kekule systems can either be coextensive or disjoint.
As we have shown in earlier studies of the 3,40-through
ꢀ
biphenyl system 152 + and 3,30-through biphenyl system
ꢀ
162 +, when hole distributions are coextensive the hole–
ꢀ
hole repulsion is bigger than in the equivalent disjoint struc-
ture.17 In the case of the coextensive 3,40-through biphenyl
system 15 this leads to difference between the first and sec-
ond oxidation potentials of w0.1 V. In the coextensive 1,3-
only disjoint radical ions (analogous to 5n +) will be formed
ꢀ
first and the coextensive species (analogous to 52n +), neces-
sary to generate high-spin character, only generated in the
final stages. Similarly, if doping is less than 100% efficient
DISJOINT
COEXTENSIVE
or
5n.+ and 122.+
52n.+
MeO
MeO
MeO
N
OMe
N
OMe
N
MeO
N
152.+
162.+
MeO
OMe
N
MeO
N
MeO
N
N
N
N
N
N
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
132.+
133.+
OMe
N
OMe
N
MeO
N
MeO
N
N
N
N
N
MeO
OMe
MeO
OMe
143.+
142.+
Figure 8. Coextensive (left) and disjoint (right) amminium radical cations and the most likely structures for the dications and trications formed from 13 and 14.

11464
R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
and breaks in the spin-coupling network are generated it is
clear that these will be disjoint discontinuities in the spin-
coupling since this gives the greatest ‘coulombic gain’.
Obviously in polymers in which the spin-coupling is
3,40-through biphenyl or 4,400-through metaterphenyl, the
coulombic ‘penalty’ for forming the coextensive radical
ions will be less than in the models 12–14 where coupling
is 1,3-through benzene. However, the exchange interaction
will also be smaller and in the 4,400-through metaterphenyl
case it proves to be so small that there are problems of ther-
mal population of low spin states.13 Overall, despite the fact
that it is easier to make triphenylamminium radical cations
than trityl radicals and in general they are more stable, these
coulombic effects make the triphenylamminium radical cat-
ion a less desirable base for high-spin polymers than the
trityl radicals. Despite several years of work by several dif-
ferent groups, the best triphenylamminium radical cation
based high-spin polymers only show clusters of 6–8 ferro-
magnetically coupled spins,4,5,9,10 whereas the best trityl
radical based high-spin polymers show up to w5000 ferro-
magnetically coupled spins.2
was checked before and after each experiment for the solvent
used. The appropriate IR compensation was applied using
the CONDECON software system. For the voltammograms
shown in Figure 3, the potential was swept in the anodic
direction (upper trace) and the lower trace represents the
reverse sweep in the cathodic direction.39
4.4. UV/visible/near IR spectroscopy
The UV spectrum of a dilute polyamine solution (ca. [6/
number of dopable sites]ꢃ10ꢁ5 mol lꢁ1) in dry dichlorome-
thane (3 cm3) in a 1 cm path length cell was recorded in the
range of 1600–250 nm. The spectrum was then recorded af-
ter each successive addition of THBF438 (2.3ꢃ10ꢁ3 mol lꢁ1
,
5–10 ml) in dichloromethane. This was done until 2 equiv of
the oxidant per dopable site had been added. Software cor-
rections were then employed to compensate for the small di-
lution caused by the addition of the oxidant. Compound 11:
lmax 305 nm, 4.07 eV (log10 3, 4.08). Compound 11ꢀ+: lmax
347 nm, 3.58 eV (log10 3, 3.80); 370, 3.36 (3.85); 512 (s),
2.44 (3.18); 594, 2.09 (3.46); 816 (s), 1.50 (3.48); 922, 1.35
(3.54). Isosbestic points 11/11ꢀ+, 273 nm; 320. Compound
12: lmax 300 nm, 4.16 eV (log10 3, 4.67). Compound 12ꢀ+:
lmax 381 nm, 3.25 eV (log10 3, 4.35); 473 (s), 2.63 (3.62);
594, 2.09 (3.46); 901 (s), 1.38 (3.56); 1107, 1.13 (3.47). Iso-
sbestic points 12/12ꢀ+, 271 nm, 331, 486. Compound 13:
lmax 301 nm, 4.13 eV (log10 3, 4.79). Compound 13ꢀ+: lmax
385 nm, 3.25 eV (log10 3, 4.26); 452, 2.73 (4.03); 987 (s),
4. Experimental
4.1. Synthesis: general procedures
Full details of the syntheses, purification,37 analytical and
spectroscopic procedures are given in Supplementary data.
The proof of the structure for the compounds (particularly
for the key tetraamines 13 and 14) rests substantially on
2-D NMR, COSY, HMQC and HMBC experiments, which
were used to assign all the carbon and hydrogen reso-
nances.38
ꢀ
1.24 (3.65); 1149, 1.06 (3.75). Compound 132 +: lmax
369 nm, 3.33 eV (log10 3, 4.38); 447, 2.80 (4.13); 987, 1.24
(3.78); 1072, 1.08 (4.05). Compound 14: lmax 300 nm,
4.15 eV (log10 3, 4.76). Compound 14ꢀ+: lmax 388 nm,
3.20 eV (log10 3, 4.18); ca. 1150, 1.18 (2.88). Compound
ꢀ
142 +: lmax 360 nm, 3.44 eV (log10 3, 4.39), ca. 1150, 1.18
(3.18).40
4.2. X-ray crystallography
4.5. Electron paramagnetic resonance
Single crystals of N,N,N0,N0-tetrakis(2-methoxyphenyl)-
benzene-1,3-diamine (12) were obtained by recrystallisation
from dichloromethane/hexane. A crystal was mounted in
inert oil and transferred to the cold gas stream of the
diffractometer. C34H32N2O4, M¼532.62, monoclinic, a¼
EPR measurements were made on an X-band ER-200
Bruker ESR spectrometer using either a simple standard
EPR tube or a sealed cell that enabled the sample to be con-
centrated or diluted under vacuum. In a typical experiment,
the EPR tube was filled with a thoroughly dried and degassed
solution of the polyamine ca. 1ꢃ10ꢁ4 mol lꢁ1 in dichloro-
methane, so that the depth of the solution in the tube spanned
the microwave cavity (ca. 0.5 cm3). The solution was cooled
to ꢁ77 ꢂC and NOBF4 (20-fold excess) was added to the
cold solution under a steady stream of argon. The solution
was sonicated for 15 min using a Kerry ultra-sound bath
operating at 50 Hz under a dry atmosphere of argon.
˚
˚
˚
9.4847(2) A, b¼12.0494(2) A, c¼24.2743(6) A, U¼
3
˚
2772.0(1) A , T¼100(2) K, space group P21/n (no. 14),
Z¼4, m¼0.084 mmꢁ1, 23,023 measured reflections, 5425
unique (R(int)¼0.058). The final wR(F2) was 0.220 (all data).
4.3. Cyclic voltammetry
These studies were carried out using a conventional three
electrode system coupled to an EG&G Model 362 scanning
potentiostat and the system was controlled by a PC unit run-
ning the ‘Condecon 320’ cyclic voltammetry software. The
working electrode was a small platinum disc, ca. 2 mm di-
ameter, the counter electrode was a platinum coiled wire
and the reference electrode, a silver wire immersed in a sat-
urated lithium chloride/dichloromethane mixture containing
the supporting electrolyte tetrabutylammonium hexafluoro-
borate (0.1 M). Prior to use, solvents were thoroughly dried
and degassed, and the concentrations for the polyamines
were approximately 1 mg cmꢁ3. The ferrocene/ferrocenium
couple was used as a standard (taken to be +0.5 V vs Ag/
AgCl under these conditions) and its oxidation potential
4.6. Magnetometry
Magnetic measurements were carried out using a SQUID
magnetometer (MPMS, Quantum Design) at the University
of Sheffield. In a typical experiment NOBF4 (1 g,
8.6 mmol, 40 mol %) was added to a thoroughly dried and
degassed stirred solution of polyamine (100 mg, ca.
0.2 mmol of dopable nitrogen sites) in dichloromethane
(300 cm3) at 0 ꢂC under an atmosphere of dry argon in
a round-bottomed Schlenk flask. The solution was sonicated
for 30 min using a Kerry ultra-sound bath operating at 50 Hz
under an argon atmosphere at 0 ꢂC. Most of the solvent was

R. J. Bushby et al. / Tetrahedron 63 (2007) 11458–11466
11465
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